The long-term consequences of methamphetamine (METH) abuse include a persistent, partial loss of monoamine systems in the brain, particularly the dopamine innervation of the striatum. Despite the apparent relative sparing of function at smaller sizes of dopamine depletion, several lines of evidence suggest that there is a significant impact of such partial dopamine loss on central nervous system function. Both abstinent METH abusers with documented decreases in dopamine uptake sites in striatum and patients early in the course of Parkinson's disease show deficits on cognitive tasks. Studies in animals with partial monoamine depletions have revealed deficits in learning and memory functions dependent on striatal, hippocampal, and cortical function, and recent data from our laboratory suggest that such deficits may be associated with impaired activation of the effector immediate early gene arc. Partial dopamine depletions also are associated with decreased dopamine concentrations evoked by electrical stimulation mimicking phasic dopamine signaling. Finally, partial monoamine depletions are associated with changes in measures of the function of striatonigral (direct pathway) efferent neurons of striatum. Taken together, these data suggest that partial dopamine depletions of striatum selectively alter striatonigral neuron function and, consequently, basal ganglia- dependent learning and memory function by impairing phasic dopamine neurotransmission. This hypothesis will be examined by 1) further characterizing the impact of METH-induced neurotoxicity on basal ganglia-mediated learning and memory processes; 2) determining whether METH-induced neurotoxicity is associated with degradation of dopamine transients and whether activating phasic dopamine transmission will selectively enhance striatonigral neuron function; and 3) examining the impact of METH-induced neurotoxicity on arc induction and cytoplasmic distribution as well as on the involvement of striatal Arc in learning and memory. Completion of these experiments will provide improved understanding of the molecular, cellular, and behavioral impact of METH-induced neurotoxicity to central dopamine systems on basal ganglia function. Such understanding will be critical to allow for the development of targeted strategies to therapeutically manage the long-term effects of such stimulant abuse. PUBLIC HEALTH RELEVANCE It is now established that methamphetamine (METH) abuse leads to long-lasting decreases in the dopamine innervation of the caudate-putamen in humans, as well as other species. The goal of this project is to further determine the impact of METH- induced neurotoxicity on basal ganglia function and basal ganglia-mediated learning and memory processes and to assess whether changes in phasic dopamine neurotransmission underlie the long-term effects of METH on basal ganglia function and behavior.